/*
 * Copyright (C) 2011 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.itranswarp.javapractice.plugin.repackaged.com.google.gson.internal;

import java.io.ObjectInputStream;
import java.io.ObjectStreamClass;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

/**
 * Do sneaky things to allocate objects without invoking their constructors.
 *
 * @author Joel Leitch
 * @author Jesse Wilson
 */
public abstract class UnsafeAllocator {
	public abstract <T> T newInstance(Class<T> c) throws Exception;

	public static UnsafeAllocator create() {
		// try JVM
		// public class Unsafe {
		// public Object allocateInstance(Class<?> type);
		// }
		try {
			Class<?> unsafeClass = Class.forName("sun.misc.Unsafe");
			Field f = unsafeClass.getDeclaredField("theUnsafe");
			f.setAccessible(true);
			final Object unsafe = f.get(null);
			final Method allocateInstance = unsafeClass.getMethod("allocateInstance", Class.class);
			return new UnsafeAllocator() {
				@Override
				@SuppressWarnings("unchecked")
				public <T> T newInstance(Class<T> c) throws Exception {
					return (T) allocateInstance.invoke(unsafe, c);
				}
			};
		} catch (Exception ignored) {
		}

		// try dalvikvm, post-gingerbread
		// public class ObjectStreamClass {
		// private static native int getConstructorId(Class<?> c);
		// private static native Object newInstance(Class<?> instantiationClass, int
		// methodId);
		// }
		try {
			Method getConstructorId = ObjectStreamClass.class.getDeclaredMethod("getConstructorId", Class.class);
			getConstructorId.setAccessible(true);
			final int constructorId = (Integer) getConstructorId.invoke(null, Object.class);
			final Method newInstance = ObjectStreamClass.class.getDeclaredMethod("newInstance", Class.class, int.class);
			newInstance.setAccessible(true);
			return new UnsafeAllocator() {
				@Override
				@SuppressWarnings("unchecked")
				public <T> T newInstance(Class<T> c) throws Exception {
					return (T) newInstance.invoke(null, c, constructorId);
				}
			};
		} catch (Exception ignored) {
		}

		// try dalvikvm, pre-gingerbread
		// public class ObjectInputStream {
		// private static native Object newInstance(
		// Class<?> instantiationClass, Class<?> constructorClass);
		// }
		try {
			final Method newInstance = ObjectInputStream.class.getDeclaredMethod("newInstance", Class.class,
					Class.class);
			newInstance.setAccessible(true);
			return new UnsafeAllocator() {
				@Override
				@SuppressWarnings("unchecked")
				public <T> T newInstance(Class<T> c) throws Exception {
					return (T) newInstance.invoke(null, c, Object.class);
				}
			};
		} catch (Exception ignored) {
		}

		// give up
		return new UnsafeAllocator() {
			@Override
			public <T> T newInstance(Class<T> c) {
				throw new UnsupportedOperationException("Cannot allocate " + c);
			}
		};
	}
}
